An iridescent silvery grey, olive-green to bluish grunter, with a silver to golden stripe below the eye, a pale to dark spot on the upper edge of the gill cover, dark fins, and sometimes 7-8 wavy stripes of varying thicknesses (the middle stripe the thickest) along the sides. Juveniles have pronounced stripes on the sides.The Lake Bonaparte Grunter has a terminal mouth, a wide, rounded U-shaped lower jaw when viewed from below, a thick, fleshy fold on the upper and lower lips, a relatively deep body, and a distinctively steep ventral profile that is straight or concave in adults and slightly convex in juveniles.

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Distribution

Endemic to rivers draining into the Joseph Bonaparte Gulf between the Carson River, Western Australia, and the Finniss River, Northern Territory.

Inhabits deeper parts of slow-flowing creeks and rivers, and billabongs - in clear and turbid waters, over muddy to rocky substrates, often with abundant algal growth, and in water temperatures to 36°C. Adults form shoals around snags and river banks, while juveniles mostly occur in riffle habitats.

Adults uniformly silver, iridescent olive green to blue, or light grey. Occasionally with 7–8 longitudinal body stripes on juveniles and adults, that quickly fade when removed from the water or after death: first running along sheath at base of spinous dorsal from third dorsal spine to third or fourth ray; second, from origin of dorsal to below soft dorsal; third, from above eye across post-temporal and then to just beyond based on last soft dorsal ray; fourth, from upper opercular spine to dorsal edge of caudal peduncle; fifth stripe widest, from back of eye across opercle to caudal fin base; sixth, from largest opercular spine to ventral edge of caudal peduncle; seventh stripe wavy, running from dorsal edge of pectoral base to rear of soft anal fin; eighth indistinct and sometimes lacking, positioned below seventh stripe from ventral edge of pectoral fin base to base of anal fin spines.

Feeding

Diet primarily consists of filamentous algae along with some detritus and invertebrates.

This species co-occurs with S. holsworthi, S. kimberleyensis, S. rastellus and S. trigonicus.

Similar Species

Differs from the similar Holsworth’s Grunter,Syncomistes holsworthi, in having a U-shaped rather than a V-shaped lower jaw when viewed from below. The Lake Bonaparte Grunter differs from all other species of Syncomistes in having the following combination of characters: lower jaw rounded anteriorly making a ‘U-shape’ when viewed from below, in juveniles and adults; mouth slightly oblique; teeth relatively broad and large, flat, asymmetric, margins convex posteriorly and straight to slightly concave anteriorly, widest point closest to midpoint of tooth, apical region tapered to slight point: body often with 7–8 slightly wavy brown stripes running horizontally along sides; usually < 11 gill rakers on the upper arch and < 30 in total; usually ≥ 6.0 teeth per mm of jaw.

Etymology

The specific name bonapartensis refers to the distribution of the species that is confined to drainages that once flowed into the paleolake, Lake Bonaparte.